Ultrasonic imaging systems are currently in use in a variety of medical and material testing applications. Several such systems include single transducers which are manually or mechanically scanned over the region to be observed. Electronic circuits serve to energize the transducer to isonify the object being scanned and to receive energy reflected from the object, generate representative signals, process the signals, and provide a visual display of the region being scanned. For example, the display may include a sector scan in which the various acoustic interfaces are displayed in a sector which corresponds to the sector being scanned.
More recently, ultrasonic scanning systems based upon the use of arrays of transducer elements rather than a single element have been developed. Such systems do not require mechanical or manual movement of the ultrasonic transducer. Among the latter developments have been systems which include a linear array of transducers which is electronically scanned to steer or direct the emitted ultrasonic wave front in a particular direction.
Received reflected energy at each of the transducers is then resolved by a system of electronically variable delays. Systems of this type lack good lateral resolution. F. L. Thurstone and O. T. von Ramm in their article entitled, "A New Ultrasonic Imaging Technique Employing Two-Dimensional Electronic Beam Steering", published in Acoustical Holography Vol. 5, Proceedings of the Fifth International Symposium on Acoustical Holography, 1974, Plenum Press, New York, describe an improvement in systems of the foregoing type. Thurstone, in addition to the electronic sector scan, use electronic focusing in the plane of the scan. This improves lateral resolution in the plane of the scan but results in no improvement in lateral resolution orthogonal to the scanned plane. Each of the transducer elements includes a separate amplifier, logarithmic compressor, variable delay line, and transducer associated therewith. Beyond the use of electronic focusing of received signal per se, some additional lateral resolution in the plane of the scan is achieved by multiplying the signals of the individual elements by using an aspheric curve for the transmit beam. This makes the system nonlinear so that undesired artifacts can be generated. The delay lines are lumped constant LC circuits with transistors taps controlled by computer. Systems of this type are rather complex and expensive.
Recent developments in the semiconductor field have offered improved delay lines known as charge coupled delay lines (CCD). However, when these delay lines are substituted for the prior art delay lines, electronic circuits must be employed to interconnect the charge coupled delay lines. A large amount of electronics is required for such systems.
The prior art does not teach compact, simple, inexpensive electronic untrasonic scanning systems.